The production of oil and depletion of a reservoir is typically not achieved by the natural energy of the reservoir alone (primary recovery). With primary recovery methods, oil may be produced as long as there is sufficient reservoir pressure to create flow into a well bore. Primary methods include the natural drive due to formation pressure and/or artificial lift accomplished by either pumps or lifting methods. Secondary recovery methods involve primary methods plus the addition of energy to the reservoir, typically in the form of forced injection of gas or liquid to replace produced fluids and maintain or increase reservoir pressure. Primary methods might only enable depletion of from 10% to 17% of an oil reservoir. Secondary methods typically can increase this amount to from 20% to 35%. If primary and secondary methods fail to achieve the desired production results, then tertiary methods might be added if field conditions warrant. Tertiary methods typically employ chemical and/or thermal techniques to lower the viscosity of the remaining oil-in-place and decrease the mobility of water. Yet despite the continued application and improvements of these conventional recovery techniques, in many instances two-thirds or more of known original oil-in-place can remain in the reservoirs.
Oil mining has been proposed to attempt to recover parts of this unrecovered oil that cannot be produced by primary, secondary, and/or tertiary methods. Oil mining techniques employ a combination of petroleum technology and mining technology. By way of example only, existing proposed oil mining techniques include one or a combination of an extraction method, a fracturing method, and/or a drainage method. The extraction method typically involves physical removal of reservoir rock in part or in whole to the surface where oil can be extracted, often by means of heating. A fracturing method typically employs blasting of the formation rock in the underground reservoir to recover oil.
The drainage method is somewhat similar to the conventional method for extracting oil from the surface, except wells are drilled from beneath or laterally from the side into the reservoir by means of mined slots and drift mining. In the drainage method, a cavity is typically provided somewhere beneath crude oil-bearing strata and is typically of a suitable size for workers and equipment to be received therein. A series of wells are then drilled upwardly or laterally into the reservoir for collecting oil by means of gravity. Secondary or tertiary methods as described above may also be utilized in addition to gravity for assisting flow of oil to a location beneath the reservoir. From there, it is pumped to the surface. Needs remain for equipment, systems, and methods for collecting crude oil from beneath an oil reservoir which flows thereto at least in part by the force of gravity.
While the invention was motivated in addressing the above identified issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.